3,346 research outputs found
From AMANDA to IceCube
The first string of the neoteric high energy neutrino telescope IceCube
successfully began operating in January 2005. It is anticipated that upon
completion the new detector will vastly increase the sensitivity and extend the
reach of AMANDA to higher energies. A discussion of the IceCube's discovery
potential for extra-terrestrial neutrinos, together with the prospects of new
physics derived from the ongoing AMANDA research will be the focus of this
paper. Preliminary results of the first antarctic high energy neutrino
telescope AMANDA searching in the muon neutrino channel for localized and
diffuse excess of extra-terrestrial neutrinos will be reviewed using data
collected between 2000 and 2003. Neutrino flux limits obtained with the
all-flavor dedicated UHE and cascade analyses will be described. A first
neutrino spectrum above one TeV in agreement with atmospheric neutrino flux
expectations and no extra-terrestrial contribution will be presented, followed
by a discussion of a limit for neutralino CDM candidates annihilating in the
center of the Sun.Comment: 15 pages, 8 figures Invited talk contribution at 5th International
Conference on Non-accelerator New Physics (NANP 05), Dubna, Russia, 20-25 Jun
200
A model for MRI contrast enhancement using T_1 agents
Contrast in MRI relies on differences in the local environment of water and is often enhanced by using contrast agents. We present a simple model for evaluating the minimal contrast agent concentration required to produce “satisfactory” contrast enhancement in magnetic resonance images. Previous strategies have been based largely on empirical results for specific systems. The present tissue contrast model (TCM) can be applied to “conventional,” targeted, or biochemically responsive agents. The model results are formulated so that only a small number of parameters are required to analyze a given scenario. The TCM is a particularly useful tool in the development of new classes of magnetic resonance contrast media. These agents will have the ability to target specific cells or tissue, and perhaps be able to report on their physiological status. As an example of the applicability of the TCM, we test it against in vivo magnetic resonance microscopy results in frog embryos that have focal cell populations labeled with contrast agent by using calibrated single-cell microinjection techniques
Ocorrência de nematóides das galhas das raizes, Meloidogyne incognita (Kofoid & White, 1919) Chitwood, 1949 e M. javanica (Treub, 1885) Chitwood, 1949 em Bracatinga Mimosa scabrella (Benth.) no Estado do Paraná.
bitstream/item/101253/1/PA-1983-Iede-OcorrenciaNematoides.pd
Bayesian calibration of a soil organic carbon model using Δ<sup>14</sup>C measurements of soil organic carbon and heterotrophic respiration as joint constraints
Soils of temperate forests store significant amounts of organic matter and
are considered to be net sinks of atmospheric CO<sub>2</sub>. Soil organic carbon
(SOC) turnover has been studied using the Δ<sup>14</sup>C values of bulk SOC
or different SOC fractions as observational constraints in SOC models.
Further, the Δ<sup>14</sup>C values of CO<sub>2</sub> that evolved during the
incubation of soil and roots have been widely used together with
Δ<sup>14</sup>C of total soil respiration to partition soil respiration into
heterotrophic respiration (HR) and rhizosphere respiration. However, these
data have not been used as joint observational constraints to determine SOC
turnover times. Thus, we focus on (1) how different combinations of
observational constraints help to narrow estimates of turnover times and
other parameters of a simple two-pool model, the Introductory Carbon Balance
Model (ICBM); (2) whether relaxing the steady-state assumption in a multiple
constraints approach allows the source/sink strength of the soil to be
determined while estimating turnover times at the same time. To this end ICBM
was adapted to model SOC and SO<sup>14</sup>C in parallel with
litterfall and the Δ<sup>14</sup>C of litterfall as driving variables. The
Δ<sup>14</sup>C of the atmosphere with its prominent bomb peak was used as a
proxy for the Δ<sup>14</sup>C of litterfall. Data from three spruce-dominated
temperate forests in Germany and the USA (Coulissenhieb II, Solling D0 and
Howland Tower site) were used to estimate the parameters of ICBM via Bayesian
calibration. Key findings are as follows: (1) the joint use of all four
observational constraints (SOC stock and its Δ<sup>14</sup>C, HR flux and its
Δ<sup>14</sup>C) helped to considerably narrow turnover times of the young
pool (primarily by Δ<sup>14</sup>C of HR) and the old pool (primarily by
Δ<sup>14</sup>C of SOC). Furthermore, the joint use of all observational
constraints made it possible to constrain the humification factor in ICBM,
which describes the fraction of the annual outflux from the young pool that
enters the old pool. The Bayesian parameter estimation yielded the following
turnover times (mean ± standard deviation) for SOC in the young pool:
Coulissenhieb II 1.1 ± 0.5 years, Solling D0 5.7 ± 0.8 years and
Howland Tower 0.8 ± 0.4 years. Turnover times for the old pool were
377 ± 61 years (Coulissenhieb II), 313 ± 66 years (Solling D0)
and 184 ± 42 years (Howland Tower), respectively. (2) At all three
sites the multiple constraints approach was not able to determine if the soil
has been losing or storing carbon. Nevertheless, the relaxed steady-state
assumption hardly introduced any additional uncertainty for the other
parameter estimates. Overall the results suggest that using Δ<sup>14</sup>C
data from more than one carbon pool or flux helps to better constrain SOC
models
RG-improved single-particle inclusive cross sections and forward-backward asymmetry in production at hadron colliders
We use techniques from soft-collinear effective theory (SCET) to derive
renormalization-group improved predictions for single-particle inclusive (1PI)
observables in top-quark pair production at hadron colliders. In particular, we
study the top-quark transverse-momentum and rapidity distributions, the
forward-backward asymmetry at the Tevatron, and the total cross section at
NLO+NNLL order in resummed perturbation theory and at approximate NNLO in fixed
order. We also perform a detailed analysis of power corrections to the leading
terms in the threshold expansion of the partonic hard-scattering kernels. We
conclude that, although the threshold expansion in 1PI kinematics is
susceptible to numerically significant power corrections, its predictions for
the total cross section are in good agreement with those obtained by
integrating the top-pair invariant-mass distribution in pair invariant-mass
kinematics, as long as a certain set of subleading terms appearing naturally
within the SCET formalism is included.Comment: 55 pages, 14 figures, 6 table
Upgrade of the Glasgow photon tagging spectrometer for Mainz MAMI-C
The Glasgow photon tagging spectrometer at Mainz has been upgraded so that it
can be used with the 1500 MeV electron beam now available from the Mainz
microtron MAMI-C. The changes made and the resulting properties of the
spectrometer are discussed.Comment: 20 pages, 12 figure
High-Energy Neutrino Astronomy
Kilometer-scale neutrino detectors such as IceCube are discovery instruments
covering nuclear and particle physics, cosmology and astronomy. Examples of
their multidisciplinary missions include the search for the particle nature of
dark matter and for additional small dimensions of space. In the end, their
conceptual design is very much anchored to the observational fact that Nature
accelerates protons and photons to energies in excess of and
eV, respectively. The cosmic ray connection sets the scale of cosmic
neutrino fluxes. In this context, we discuss the first results of the completed
AMANDA detector and the reach of its extension, IceCube. Similar experiments
are under construction in the Mediterranean. Neutrino astronomy is also
expanding in new directions with efforts to detect air showers, acoustic and
radio signals initiated by super-EeV neutrinos.Comment: 9 pages, Latex2e, uses ws-procs975x65standard.sty (included), 4
postscript figures. To appear in Proceedings of Thinking, Observing, and
Mining the Universe, Sorrento, Italy, September 200
Visualizing Diffusion Tensor Images of the Mouse Spinal Cord
Within biological systems water molecules undergo continuous stochastic Brownian motion. The rate of this diffusion can give clues to the structure of underlying tissues. In some tissues the rate is anisotropic - faster in some directions than others. Diffusion-rate images are second-order tensor fields and can be calculated from diffusion-weighted magnetic resonance images. A 2D diffusion tensor image (DTI) and an associated anatomical scalar field, created during the tensor calculation, define seven dependent values at each spatial location. Understanding the interrelationships among these values is necessary to understand the data. We present two new methods for visually representing DTIs. The first method displays an array of ellipsoids where the shape of each ellipsoid represents one tensor value. The novel aspect of this representation is that the ellipsoids are all normalized to approximately the same size so that they can be displayed in context. The second method uses concepts from oil painting to represent the seven-valued data with multiple layers of varying brush strokes. Both methods successfully display most or all of the information in DTIs and provide exploratory methods for understanding them. The ellipsoid method has a simpler interpretation and explanation than the painting-motivated method; the painting-motivated method displays more of the information and is easier to read quantitatively. We demonstrate the methods on images of the mouse spinal cord. The visualizations show significant differences between spinal cords from mice suffering from Experimental Allergic Encephalomyelitis (EAE) and spinal cords from wild-type mice. The differences are consistent with pathology differences shown histologically and suggest that our new non-invasive imaging methodology and visualization of the results could have early diagnostic value for neurodegenerative diseases
Measurement of the 6Li(e,e'p) reaction cross sections at low momentum transfer
The triple differential cross sections for the 6Li(e,e'p) reaction have been
measured in the excitation energy region from 27 to 46 MeV in a search for
evidence of the giant dipole resonance (GDR) in 6Li. The cross sections have no
distinct structures in this energy region, and decrease smoothly with the
energy transfer. Angular distributions are different from those expected with
the GDR. Protons are emitted strongly in the momentum-transfer direction. The
data are well reproduced by a DWIA calculation assuming a direct proton
knockout process.Comment: 19 pages, 7 figures, revised text, to be published in Nucl. Phys.
A photon calorimeter using lead tungstate crystals for the CEBAF Hall A Compton polarimeter
The performances of the calorimeter of the Jlab Hall A Compton Polarimeter
have been measured using the Mainz tagged photon beam.Comment: 13 page
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